Add development server

src/refresh_websocket.js

@@ -0,0 +1,36 @@
+(function () {
+  "use strict";
+
+  console.log("Connecting...");
+
+  let socket;
+
+  function start(reload) {
+    socket = new WebSocket("ws://127.0.0.1:8080");
+    let reloading = false;
+    socket.onmessage = function (ev) {
+      if (ev.data === "reload") {
+        reloading = true;
+        console.log("Reloading...");
+        location.reload();
+      }
+    };
+    socket.onclose = function () {
+      if (!reloading) {
+        console.error("Connection closed.");
+        setTimeout(() => {
+          console.log("Retrying connection...");
+          start(true);
+        }, 2000);
+      }
+    };
+    socket.onopen = function () {
+      console.log("Connected!");
+      if (reload) {
+        location.reload();
+      }
+    };
+  }
+
+  start(false);
+})();